class Logger

• Logger
• Reference
• Object

Overview

The Logger class provides a simple but sophisticated logging utility that you can use to output messages.

The messages have associated levels, such as INFO or ERROR that indicate their importance. You can then give the Logger a level, and only messages at that level or higher will be printed.

For instance, in a production system, you may have your Logger set to INFO or even WARN. When you are developing the system, however, you probably want to know about the program’s internal state, and would set the Logger to DEBUG.

Example

require "logger"

log = Logger.new(STDOUT)
log.level = Logger::WARN

# or
log = Logger.new(STDOUT, level: Logger::WARN)

log.debug("Created logger")
log.info("Program started")
log.warn("Nothing to do!")

begin
  File.each_line("/foo/bar.log") do |line|
    unless line =~ /^(\w+) = (.*)$/
      log.error("Line in wrong format: #{line}")
    end
  end
rescue err
  log.fatal("Caught exception; exiting")
  log.fatal(err)
end

If logging to multiple locations is required, an IO::MultiWriter can be used.

file = File.new("production.log", "a")
writer = IO::MultiWriter.new(file, STDOUT)

log = Logger.new(writer)
log.level = Logger::DEBUG
log.debug("Created logger")

Defined in:

Constant Summary

DEBUG = Severity::DEBUG

ERROR = Severity::ERROR

FATAL = Severity::FATAL

INFO = Severity::INFO

UNKNOWN = Severity::UNKNOWN

WARN = Severity::WARN

Constructors

• .new(io : IO | Nil, level : Logger::Severity = Severity::INFO, formatter : Logger::Severity, Time, String, String, IO -> _ = DEFAULT_FORMATTER, progname : String = "")

  Creates a new logger that will log to the given io.

Instance Method Summary

• #close

  Calls the close method on the object passed to initialize.

• #debug(message, progname = nil)

  Logs message if the logger's current severity is lower or equal to DEBUG.

• #debug(progname = nil, &)

  Logs the message as returned from the given block if the logger's current severity is lower or equal to DEBUG.

• #debug?

  Returns true if the logger's current severity is lower or equal to DEBUG.

• #error(message, progname = nil)

  Logs message if the logger's current severity is lower or equal to ERROR.

• #error(progname = nil, &)

  Logs the message as returned from the given block if the logger's current severity is lower or equal to ERROR.

• #error?

  Returns true if the logger's current severity is lower or equal to ERROR.

• #fatal(message, progname = nil)

  Logs message if the logger's current severity is lower or equal to FATAL.

• #fatal(progname = nil, &)

  Logs the message as returned from the given block if the logger's current severity is lower or equal to FATAL.

• #fatal?

  Returns true if the logger's current severity is lower or equal to FATAL.

• #formatter : Logger::Severity, Time, String, String, IO -> Nil

  Customizable Proc (with a reasonable default) which the Logger uses to format and print its entries.

• #formatter=(formatter : Logger::Severity, Time, String, String, IO -> _)

  Customizable Proc (with a reasonable default) which the Logger uses to format and print its entries.

• #info(message, progname = nil)

  Logs message if the logger's current severity is lower or equal to INFO.

• #info(progname = nil, &)

  Logs the message as returned from the given block if the logger's current severity is lower or equal to INFO.

• #info?

  Returns true if the logger's current severity is lower or equal to INFO.

• #level : Severity
• #level=(level : Severity)
• #log(severity, message, progname = nil) : Nil

  Logs message if severity is higher or equal with the logger's current severity.

• #log(severity, progname = nil, &) : Nil

  Logs the message as returned from the given block if severity is higher or equal with the loggers current severity.

• #progname : String
• #progname=(progname : String)
• #unknown(message, progname = nil)

  Logs message if the logger's current severity is lower or equal to UNKNOWN.

• #unknown(progname = nil, &)

  Logs the message as returned from the given block if the logger's current severity is lower or equal to UNKNOWN.

• #unknown?

  Returns true if the logger's current severity is lower or equal to UNKNOWN.

• #warn(message, progname = nil)

  Logs message if the logger's current severity is lower or equal to WARN.

• #warn(progname = nil, &)

  Logs the message as returned from the given block if the logger's current severity is lower or equal to WARN.

• #warn?

  Returns true if the logger's current severity is lower or equal to WARN.

Constructor Detail

Instance Method Detail

require "logger"

logger = Logger.new(STDOUT)
logger.progname = "YodaBot"

logger.formatter = Logger::Formatter.new do |severity, datetime, progname, message, io|
  label = severity.unknown? ? "ANY" : severity.to_s
  io << label[0] << ", [" << datetime << " #" << Process.pid << "] "
  io << label.rjust(5) << " -- " << progname << ": " << message
end

logger.warn("Fear leads to anger. Anger leads to hate. Hate leads to suffering.")

# Prints to the console:
# "W, [2017-05-06 18:00:41 -0300 #11927]  WARN --
#  YodaBot: Fear leads to anger. Anger leads to hate. Hate leads to suffering."

require "logger"

logger = Logger.new(STDOUT)
logger.progname = "YodaBot"

logger.formatter = Logger::Formatter.new do |severity, datetime, progname, message, io|
  label = severity.unknown? ? "ANY" : severity.to_s
  io << label[0] << ", [" << datetime << " #" << Process.pid << "] "
  io << label.rjust(5) << " -- " << progname << ": " << message
end

logger.warn("Fear leads to anger. Anger leads to hate. Hate leads to suffering.")

# Prints to the console:
# "W, [2017-05-06 18:00:41 -0300 #11927]  WARN --
#  YodaBot: Fear leads to anger. Anger leads to hate. Hate leads to suffering."